Control in the Field
For all the fieldbus installations in the world, I would be surprised if 20 percent were actually using control in the field, which was the original intention of a fieldbus infrastructure -- to provide truly distributed control. Devices today do seem extremely reliable, why aren't more users putting control in the field? I'd be ionterested to hear your opinions. I think it is as much an issue of anxiety and refusal to let go of the old way of doing things.
I wasn't sure where to put this topic. Also, it would be nice to have a search engine on this site.
Larry
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Agree with Dan . . . my $0.02
When I go to ISA conferences and / or FF workshops I sometimes ask "how many here are doing DCS configuration". It is rare to get any show of hands.
I haven't had anyone from ABB, Honeywell, or Yokogawa call on me in years, but my opinion is that uptake of control-in-the-field is sluggish because it was never marketed to systems people. Although we have a lot of suggestions for our suppliers, end users really rely on them for some leadership, especially in "new" technology areas. BP had Richard Willems (now with Honeywell) in the Lima plant early on (ca. 1999), when we were pondering whether to implement CIF, and we spent the better part of a day peppering him with all of our misgivings about it. He was an excellent missionary and we ended up implementing CIF for the majority of control loops.
I get the impression - correct or not - that host supplier sales people are either 1) Focused on other host features 2)Just plain ignorant about FF 3)Reluctant to promote a feature that their competitor excels at. 4)Still dealing with "turf" issues between device guys & system people. Whatever - the message (CIF is good and you should try it) doesn't seem to have penetrated a lot of end-user and EPC firm "systems group" organizations . . .
At Emerson Exchange, I would be interested to see the presenters at the FF sessions pose the question I do - "how many in the room have "DCS Configuration" or "Systems Sales" as one of your primary responsibilities?"
John Rezabek
ISP Lima LLC
Fieldbus Control in the field
I am one of those who had mixed feelings until fairly recently about putting the PID control block into a FF field device. But for fairly different reasons.
Back in 2000-2001 time frame, we implemented one segment of Fieldbus with a pressure transmitter (this was just for pressure indication) a flow transmitter and a flow control valve (part of the flow control loop). The PID control was implemented in the DCS. With the amount of diagnostics information available (and how it could be interpreted in the DCS) back in 2000-2001 time frame, it was not an easy task. To make matters worse the flow transmitter sensor was way oversized due to miscalculations in estimating what the flow would be. With the operators and process engineers not trusting the flow loop and with my difficulty in trying to tune the loop with such low flow, there was a lot of mixed feelings about FF devices. Unlike traditional transmitters which can be re-ranged for a different flow, the FF transmitter could not be re-ranged (I remember having long conversations with the transmitter vendor about this). As much as I believed in Fieldbus technology (and the fact that the pressure transmitter was working fine), I could not convince the production folks that we could eventually make this flow control loop work. Anyway, the end result was that this particular production unit decided to rip out the Fieldbus segment completely and replace all devices with traditional HART devices.
I have worked in another unit (at the same plant location) where we have installed and configured many Fieldbus devices. The applications are mostly Tank Farm type with 95% of the devices being used only for indication. Now we have started to add valves into several of the loops. But the PID control is still in the DCS. I am sure we will move away from this practice and start implementing the PID block in the field devices fairly soon. There are obvious advantages to doing this as most of you know.
If I look back at these two production units in how they embraced or mistrusted Fieldbus devices, the lesson learnt for me is "start with very simple and straight forward applications that will work and then slowly go towards more complex uses". The project team in one case (I was part of the team) made the mistake of trying to implement a Control Loop/PID with brand new technology and failed. The project team in the second case (I was not part of the team but was heavily involved in making decisions) started with very simple applications like Tank Levels, Temperatures, Pressures (indication only)and then slowly moved into adding control (valves).
I am sure a lot of DCS/Instrumentation vendors or engineers from EPC firms will laugh at me for being "So Slow" in adopting new technology. But, as an end user, I look at this as an acceptance that has to come from everyone (DCS engineers, Instrument technicians and especially the operator who has to live with "I can trust this" or "I cannot trust this").
Thoughts from Emerson Fieldbus Consultant, Dan Daugherty
Emerson's fieldbus consultant, Dan Daugherty, has these thoughts to share:
Part of it is a holdover from the old ways. If you do control-in-controller, and you don’t care a whole lot about process segregation (only do it on a coarse, controller level), then you can skip all the concerns regarding segment design except for voltage drop and number of devices. Many engineering companies didn’t want to learn segment design, so they stuck with control-in-controller.
The second reason is that occasionally, some control strategies are complex enough they can’t be done on a single segment (prior to 2007) because not all the control functions they wanted to use were available in devices. That is no longer true with Emerson because we have ability to pick up functions in the H1 card, effectively filling out any gaps that used to exist in the control-in-field palette of functions. However, that is only Emerson, and it is only in last couple of years, so it doesn’t represent a large percentage of applications, especially if you go back to the beginning of fieldbus deployment.
It is also my opinion that manufacturers other than Emerson employed add-on (non-native) fieldbus solutions, so they weren’t pushing control-in-field, and some of them either didn’t do it well, or experienced some loss of capacity in the controller when control-in-field was used.
There are economic and performance advantages to using control-in-field. That is why Emerson has promoted it, and in fact made it better by adding the ability to execute synchronized functions in the H1 card. We will be presenting a paper at Emerson Exchange this year where we compare performance of control-in-field against control-in-controller by showing results of tests we did on a flow loop in one of our flow labs in Marshalltown. We believe the economic advantages are obvious – more devices per segment for a given update rate, and that in turn leads to fewer I/O cards and less cabinet space in the equipment room.
CENTUM FF
I do know that the Yokogawa Centum implementation of FF is nearly seamless and can provide both 100% CIP or a combination.
We have implemented some loops with FF CIP, all the logic design was conducted from within the normal CENTUM engineering display in the same drawing as traditional control logic.
I agree with everyones sentiments here, the only thing holding back FF CIP is user sentiment. But it is definately changing for the better.